This invention relates to a method and a device, such as an electromagnet, for generating in a hollow space a magnetic field derived from a static magnetic potential.
A device of the type described is used in a corpuscular-ray analyser, a particle accelerator, a corpuscular-ray bending and/or focusing device, a plasma producing device, or the like in controlling the path of charged particles. As will later be described with reference to a few figures of the accompanying drawing, a conventional device of the type described has to be precisely machined during manufacture and is unduly bulky as compared with the space in which the magnetic field is to be generated. Furthermore, it is difficult with a conventional device of the type described to adjust the magnetic field and to render the space sufficiently wide.
According to Applicant's prior invention which is disclosed in a Japanese patent application filed Aug. 21, 1975, and published Feb. 25, 1977, a device of the type described is proposed whereby a 2N pole magnetic field is generated in a substantially rectangular, rhombic, square, or equilateral hexagonal or octagonal prismal space. A device according to the prior invention comprises a hollow prismal yoke having 2N inside lateral surfaces. Conductors are extended axially along the respective inside lateral surfaces of the space and at least inwardly of the lateral surfaces. When the yoke is of a hollow rectangular prismal shape, use is made of a rectangular x-y coordinate system with the x and y axes perpendicularly bisecting x and y inside surfaces, respectively. Density of the conductors arranged along the x and y inside surfaces is given by y.sup.N-2 and x.sup.N-2, respectively. When the yoke is of a hollow rhombic prismal shape, N should be equal to three or more. A sextipole and an octopole magnetic field may be produced by the use of a hollow hexagonal and a hollow octagonal prismal yoke respectively. The prior invention also provides a combination of devices for producing 2N-pole magnetic fields wherein the number N is adjusted to provide a first through an (N-1)-th order convergence for a charged particle beam.
With a device according to the prior invention, it is possible to avoid the precise machining, to render the device astonishingly compact, to adjust the magnetic field, and to widen the space. It is, however, impossible to provide a static magnetic field of a more general distribution in a hollow space of an optional shape. Furthermore, the conductors arranged inwardly of the yoke inside surface restrict the space in which the magnetic field is produced.